1. Field of the Invention
The present invention relates to a key assigner, for an electronic musical instrument, that assigns tone generation to a predetermined oscillator upon the reception of a tone-ON command from a keyboard or an external device.
Tone generators for recent electronic musical instruments have a plurality of oscillators, and drive the oscillators, which are combined as needed, to enable the simultaneous production of a plurality of musical tones.
A timbre for tone production is obtained by providing timbre data to an oscillator. However, as the effect of a timbre that is produced using a single oscillator is limited, and as a timbre that has a desired quality cannot at times be thus obtained, a tone generator has been developed, and is in current practical use, that simultaneously drives a plurality of oscillators to generate a desired timbre.
In an electronic musical instrument that incorporates such a tone generator, tone production often involves the employment both of timbres generated by a single oscillator (hereafter referred to as "one-source timbres") and of timbres generated by a plurality of oscillators (hereafter referred to as "multi-source timbres").
As the number of multi-source timbres increases, the number of musical tones that can be simultaneously produced is correspondingly reduced. A desirable key assigner for an electronic musical instrument, therefore, is one that can efficiently employ a limited number of oscillators to maximize the number of musical tones that can be simultaneously produced.
2. Description of the Related Art
Conventionally, those electronic musical instruments that can process multi-source timbres employ a constant number of oscillators to produce the multi-source timbre. An electronic musical instrument having eight oscillators, for example, constantly employs two oscillators to produce one timbre.
Therefore, when production of a timbre is required, two oscillators must always be allocated even when only a single oscillator would suffice, and the total number of musical tones that can be simultaneously produced by the electronic musical instrument is reduced.
More specifically, even though the generation of a timbre A requires two oscillators but the production of a timbre B requires only one, the subject electronic musical instrument will assign two oscillators for the generation of either timbre. Consequently, the number of musical tones that the electronic musical instrument can simultaneously produce is limited to four.
An electronic musical instrument that can adequately manage multi-source timbres assigns timbre generation tasks to individual oscillators. Thus, when two oscillators are required for generation of a timbre, two oscillator assignments are performed.
Accordingly, when many one-source timbres are generated, the number of musical tones that can be simultaneously produced increases. Thus, in the above example, when the generated timbres are all of type timbre B, the number of musical tones that can be simultaneously produced is eight.
Since, however, for the generation of a multi-source timbre, individual assignment processing for multiple oscillators is required, the time lapse between the reception of a tone-ON command and the actual tone production by all the oscillators is extended compared to that for the generation of a one-source timbre.